全文获取类型
收费全文 | 34033篇 |
免费 | 6043篇 |
国内免费 | 8162篇 |
专业分类
测绘学 | 2635篇 |
大气科学 | 7065篇 |
地球物理 | 8489篇 |
地质学 | 16437篇 |
海洋学 | 3944篇 |
天文学 | 1437篇 |
综合类 | 3790篇 |
自然地理 | 4441篇 |
出版年
2024年 | 123篇 |
2023年 | 447篇 |
2022年 | 1493篇 |
2021年 | 1697篇 |
2020年 | 1368篇 |
2019年 | 1653篇 |
2018年 | 1867篇 |
2017年 | 1712篇 |
2016年 | 1961篇 |
2015年 | 1726篇 |
2014年 | 2076篇 |
2013年 | 2038篇 |
2012年 | 1968篇 |
2011年 | 2030篇 |
2010年 | 2147篇 |
2009年 | 2026篇 |
2008年 | 1888篇 |
2007年 | 1790篇 |
2006年 | 1379篇 |
2005年 | 1303篇 |
2004年 | 996篇 |
2003年 | 988篇 |
2002年 | 935篇 |
2001年 | 995篇 |
2000年 | 1162篇 |
1999年 | 1552篇 |
1998年 | 1232篇 |
1997年 | 1178篇 |
1996年 | 1111篇 |
1995年 | 958篇 |
1994年 | 835篇 |
1993年 | 743篇 |
1992年 | 587篇 |
1991年 | 467篇 |
1990年 | 346篇 |
1989年 | 324篇 |
1988年 | 284篇 |
1987年 | 161篇 |
1986年 | 146篇 |
1985年 | 93篇 |
1984年 | 101篇 |
1983年 | 73篇 |
1982年 | 69篇 |
1981年 | 57篇 |
1980年 | 36篇 |
1979年 | 33篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1958年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
The subtle interactions between the magnetohydrodynamics (MHD) and transverse plasmons are investigated. It is shown that there is a resistive instability by the plasmon's soliton in a current sheet, which eventually turns into an eruptive instability at the magnetic field reconnection. In the case of ion-acoustic turbulence, the high temperature current sheet model must adopt the aromalous conductivity instead of the Coulomb conductivity. The numerical results are consistent with the observations obtained by Hanaoka (1994). Thus the flare caused by X-ray loop coalescence can be basically interpreted by this model of magnetic field reconnection driven by ponderomotive force. 相似文献
103.
以首都圈地区现今活动断层上近20年的位移测量资料为依据,用二维线弹性有限元对该区断层的活动特征进行了拟合,并结合有关资料讨论了该区的地震危险性。结果表明:1977-1986年间该区主压应力优势方位与华北较一致,约为N45°-80°E;1986-1990年其主压应力方向向北偏转,约为N5°-60°E;1990年至现在其主压应力又向东偏转,角度大于第一阶段,约为N80°-95°E。该区的张家口-延庆一带近期有发生中强震的可能;丰镇-阳高-大同地区和凉城-古营盘地区应力较高,也应引起注意。 相似文献
104.
The masers of E-type methanol in orion KL and SGR B2 总被引:2,自引:0,他引:2
Using a simplified model the statistical equilibrium and radiative transfer equations of E-type-CH3OH are solved for Orion KL and SgrB2. According to our calculation results and the observation data taken by Matsakiset al. (1980) and Morimotoet al. (1985a, b), the physical conditions of both sources are estimated. In theJ
2-J
1 E methanol maser region of Orion KL, the density, kinetic temperature, dust temperature, and the fractional abundance are 0.8–2×106 cm–3, 150, 30–90 K, 0.8–8×10–6. In the 4–1-30 E and 5–1-40 E methanol maser region of Sgr B2 the correspondance physical conditions above are 104 cm3, 45, 23 K, and 7×10–7, respectively. 相似文献
105.
106.
提出川滇地洼系“四层楼”铜矿床序列的形成与陆壳演化的成生联系,是与本区陆壳由前地槽—地槽—地台—地洼演化各阶段与之相匹配的成矿作用的产物.与此同时,并总结了本区“四层楼”铜矿床序列的成矿作用具有明显的继承性、新生性、旋回性及层控性四大特点和多因复成矿床的成矿模式. 相似文献
107.
The data such as the H-spectrum-spectroheliographic (SSHG) observations, the H-chromospheric observations, etc., of a flare loop prominence which occurred on the western solar limb on 1981 April 27 have been obtained at Yunnan Observatory. The distribution of the internal motions and the macroscopical motion of the flare loop prominence with time and space in the course of its eruption and ascension is derived from the comprehensive analysis of the data. The possible physical pictures and the instability of the motions of the loop are inferred and discussed. 相似文献
108.
Soil nails have been widely used to stabilize slopes and earth retaining structures in many countries and regions, especially, in Hong Kong. The analysis of the interaction between a soil nail and the surrounding soil is of great interests to both design engineers and researchers. In this paper, authors present a simple mathematical model for the interaction analysis of a soil nail and the surrounding soil considering a few key factors which are soil dilation, bending of the soil nail, vertical pressure, and non-linear subgrade reaction stiffness. The lateral subgrade reaction between the soil and the soil nail is assumed to obey a hyperbolic relation. Reported test data in the literature are used to verify the present model. The contributions of the soil-nail bending on the pull-out resistance are evaluated in two case studies. 相似文献
109.
Maggie Cusack Yannicke Dauphin Jean-Pierre Cuif Murielle Salom Andy Freer Huabing Yin 《Chemical Geology》2008,253(3-4):172-179
Biominerals are natural composite materials comprising organic and inorganic components. Detailed knowledge of the nature and distribution of both components is a crucial requirement in order to advance our understanding of biomineral formation, their material properties and preservation potential as well as the interpretation of environmental data. Detailed chemical data are essential for our understanding of the nature and distribution of such components. Micro-XANES mapping at the sulphur K-edge reveals that, in the brachiopod Terebratulina retusa, the sulphate concentration is higher in the outer (primary) layer than in the calcite fibres of the secondary layer. This is co-incident with a higher magnesium concentration. In contrast, the sheaths surrounding the calcite fibres contain sulphur as thiol, confirming the presence of protein while, the sulphur within the fibres themselves, occurs as sulphate. Micro-XANES analysis of the insoluble organic extract from T. retusa indicates the presence of organic sulphate while Micro-Raman spectroscopy confirms that structurally substituted sulphate (SSS) is also present although semi-quantitative Raman spectroscopy carried out in this spectral region (wavenumbers 900–1200) indicates that the sulphate present is at the threshold of detection by Raman spectroscopy. The distribution of phosphorus in the shell of T. retusa correlates well with that of protein indicating the presence of phosphorylated proteins in the periostracum, the sheaths surrounding the calcite fibres and the interface between the primary and secondary layer. 相似文献
110.
Controlling of landsides safely and economically is a great challenge to mine operators because landslides are major geological
problems especially in open-pit mines. In this paper, a case history at Panluo open-pit mine is presented in detail to share
the experiences and lessons with mine operators. Panluo open-pit mine is located in the southwestern Fujian province of China.
It is the largest open-pit iron mine in the Fujian province and was planned in 1965 and is in full operation from 1978. In
July 1990, an earthquake of magnitude 5.3 in Taiwan Strait and big rainstorms impacted the mine slope, causing tension cracks
and rather large-scale failures, and forming a U-shaped landslide. Total potential volume was estimated to be up to 1.0 × 106 m3. This directly threatened the mine production. In order to protect the mine production and the dwellers’ safety around, a
dynamic comprehensive method was implemented including geotechnical investigations, in-situ testing and monitoring, stability
analysis, and many mitigation and preventive measures. These measures slowed down the development and further occurrence of
the landslide. The results showed that the landslides were still active, it was slowed with the control measures and moved
rapidly with rainfall and mining down. However, no catastrophic accidents occurred and the pit mining was continued till it
was closed at the elevation of 887 m in 2000. As a successful case of landslide control at an open-pit mine for 10 years,
this paper reports the controlling measures in details. These experiences of landslide control may be beneficial to other
similar mines for landslide control. 相似文献